Lighting controller, a lighting system and a method for controlling lighting

ABSTRACT

The invention provides a lighting controller, comprising: a detector adapted to detect a voltage of a power source, said power source is for providing power to a lighting unit via a lighting driver; a controlling unit, coupled to the lighting driver and adapted for controlling the driver to deliver a constant power to the lighting unit regardless of the power source is being consumed, before the detected voltage drops below a first threshold, and controlling the driver to deliver a gradually reduced power to the lighting unit after the detected voltage drops below the first threshold. Wherein the controlling unit is further adapted for switching an up-converter between the power source and the driver to boost the output voltage from the power source to the driver, in a first condition; and bypassing said up-converter, in a second condition, and implementing said step of controlling the driver; wherein said first condition comprises operating in high occupancy periods, and said second condition comprises operating in low occupancy period.

FIELD OF THE INVENTION

This invention relates to a lighting controller, and particularlyrelates to a lighting controller which dims the light according to stateof the energy source.

BACKGROUND OF THE INVENTION

To reduce the energy consumption per day in outdoor lighting system,light output is reduced or dimmed during non-occupancy or lowutilization period such as in the middle of night. There are variousmethods in prior art to achieve dimming e.g. presence based dimming,time based dimming etc. These dimming methods are employed on individuallighting units or at group level. Most common dimming profile employedare time based dimming e.g. full brightness between dusk to 11 PM and20-30% dimming from 11 PM to dawn. Dimming control is built in eachlighting system in decentralized solar system. In prior art; incentralized system individual lighting units are communicated throughwire or wireless i.e. PLC or zig bee or RF communication, but these arecomplex & costly. Additionally in some applications “time based dimmingprofile” is built in individual lamps. In these applications, it is verydifficult to alter the dimming profile. Further, they need RTOS(real-time operating system) based system otherwise timer will vary fromone lamp unit to another.

We also know that the overall system efficiency decreases significantlyat lower dimming levels in AC grid due to decrease in efficiency of theinverter. Therefore, DC grid is becoming more popular. Though DC grid isbetter than AC grid, they also suffer efficiency loss when operated atlower dimming level due to decrease in efficiency of LED drivers. Theseresult in higher PV and battery capacity and in turn results in highersystem cost. Therefore, there is need of low cost efficient dimmableoutdoor lighting system.

In the prior art, the lamps are usually operating at a constant power todeliver a constant lumen output despite the power source/battery state.If the battery is completely consumed, a black out occurs and thelighting system can not emit any light, which is very dangerous andinconvenient for the users. Thus it would be advantageous to have a moresophisticated lighting control mechanism that avoids black out.

U.S. Pat. No. 5,140,229A1 discloses that constant power control with therated power is effected when the supply voltage is high and power lowerthan the rated power is supplied to the metal halide lamp in accordancewith the reduction in power supply voltage.

EP1465395A2 discloses there is an up-converter that can be bypassed orswitched on according to the output of the voltage source.

SUMMARY OF THE INVENTION

It would be advantageous to switch the up-converter in a more flexibleway according to the real environment. To address at least the aboveconcern, the invention is defined by the claims.

According to a first aspect of the invention, it is provided a lightingcontroller, comprising: a detector adapted to detect a voltage of apower source, said power source is for providing power to a lightingunit via a lighting driver; and a controlling unit, coupled to thelighting driver and adapted for controlling the driver to deliver aconstant power to the lighting unit regardless of the power source isbeing consumed, before the detected voltage drops below a firstthreshold, and controlling the driver to deliver a gradually reducedpower to the lighting unit after the detected voltage drops below thefirst threshold; the controlling unit is further adapted for switchingan up-converter between the power source and the driver to boost theoutput voltage from the power source to the driver, in a firstcondition; and bypassing said up-converter, in a second condition, andimplementing said step of controlling the driver. Said first conditioncomprises operating in high occupancy periods, and said second conditioncomprises operating low occupancy periods.

In this aspect, when the power source still has sufficient energy, aconstant power is drawn and delivered by the driver to the lightingunit, thus a constant lumen output can be provided; when the availableenergy in the power source drops below a threshold, in order to avoid acomplete consumption of the power source and black out of the lightingunit, a gradually reduced power is drawn by the driver, and achieves aprolonged brown out lighting service which can at least partiallysatisfy the users. This aspect is a sophisticated combination ofconstant power load and non-constant power load. This aspect providesanother lighting mode to provide more output lumen for the lighting unitwherein the voltage from the power source is boosted/up-converted beforeto the driver. And when no need for high output, the up-converter isbypassed to reduce the voltage to the driver, and also to save theswitching loss of the up-converter. High occupancy periods require morelight thus the up-converter is in the power loop; low occupancy periodsdo not need much light thus the up-converter is bypassed.

In a further embodiment, the driver is a switched mode power source. Andsaid controlling unit is adapted for: maintaining or increasing a dutycycle of the driver so as to control the driver to deliver a constantpower; and maintaining or decreasing the duty cycle of the driver so asto control the driver to deliver a gradually reduced power.

In this embodiment, when available energy in the power source is stillsufficient, as the power source is being consumed, its output voltagewill be maintained or gradually decreased, and the driver can maintainor increase its duty cycle to deliver the constant power. When theavailable energy in the power source is not sufficient, as the powersource is being consumed, its output voltage will be graduallydecreased, meanwhile the duty cycle is maintained or even decreased,thus power will be drawn from the power source in a gradually decreasedway. Alternatively, the driver can also be linear driver and thecontrolling unit may control the conductivity of the linear power switchin order to control the power delivered by the driver.

In a still further embodiment, the controlling unit is further adaptedfor fine tuning the duty cycle of the driver such that the driverdelivers the gradually reduced and unfluctuated power to the lightingunit, after the detected voltage drops below a second threshold lessthan said first threshold.

When the power source such as battery is further consumed, its outputvoltage sometimes fluctuates, in this case if the duty cycle is stillmaintained, fluctuated power is delivered to the lighting unit thusflicker will occur. To address this concern, when the energy level inthe power source is very low, this embodiment allows fine tuning theduty cycle of the driver such that the driver delivers the unfluctuatedpower. This can avoid flicker which is not comfortable for the user thusthe user's experience would be better.

In a more specific embodiment, said high occupancy period comprisesevening till or before mid-night, and low occupancy periods comprisesmid-night till dawn.

This embodiment provides the application context of the invention.

In a further embodiment, the controlling unit is further adapted tocontrol the duty cycle of the up-converter, the up-converter comprisesan isolated boost converter, and the controlling unit further comprisesa diode forwarded between the input and the output of the up-converter.

In this embodiment, the boost converter can be bypassed by the diodeautomatically if the output voltage is no higher than the input voltagefrom the power source, thus the circuit structure is very simple.

In alternative embodiment, the controller is further adapted to controlthe duty cycle of the up-converter, the up-converter comprises anon-isolated boost converter wherein the controlling unit furthercomprises a boost diode forwarded from the connection point of aninductor and a switch of the boost converter to an output capacitor ofthe boost converter.

In this embodiment, the boost converter can be bypassed if the switch ofthe boost converter is kept open, thus the circuit structure is verysimple.

In a second aspect of the invention, a system comprising the abovecontroller is provided: a lighting system, comprising: a power source;an up converter coupled with the power source; a driver coupled to theup converter; a lighting unit coupled to the driver; and a lightingcontroller according to the first aspect, coupled to power source andthe driver.

In a third aspect of the invention, it is provided a method forcontrolling lighting, comprising the steps of: detecting a voltage of apower source, said power source is for providing power to a lightingunit via a lighting driver; controlling the driver to deliver a constantpower to the lighting unit regardless of the power source is beingconsumed before the detected voltage drops below a first threshold,controlling the driver to deliver a gradually reduced power to thelighting unit after the detected voltage drops below the firstthreshold; switching an up-converter between the power source and thedriver to boost the output voltage from the power source, in a firstcondition; and bypassing said up-converter, in a second condition, andimplementing said step of controlling; wherein said first conditioncomprises operating in high occupancy periods, and said second conditioncomprises operating in low occupancy periods.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with referenceto the accompanying drawings, in which:

FIG. 1 shows a schematic block diagram of a lighting system according anembodiment of the invention;

FIG. 2 shows a timing flowchart for the lighting system to switch itslight output according to the day/evening/night time;

FIG. 3 shows a state transition diagram for the lighting system to dimits light output according to voltage of the power source;

FIG. 4 shows an exemplified LED driver in the lighting system accordingan embodiment of the invention;

FIG. 5 shows an exemplified up-converter in the lighting systemaccording an embodiment of the invention;

FIG. 6 shows an alternative exemplified up-converter in the lightingsystem according an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a lighting controller, comprising:

a detector adapted to detect a voltage of a power source, said powersource is for providing power to a lighting unit via a lighting driver;

a controlling unit, coupled to the lighting driver and adapted for

-   -   controlling the driver to deliver a constant power to the        lighting unit regardless of the power source is being consumed,        before the detected voltage drops below a first threshold, and    -   controlling the driver to deliver a gradually reduced power to        the lighting unit after the detected voltage drops below a first        threshold.

Preferably, the controlling unit is further adapted for

-   -   switching an up-converter between the power source and the        driver to boost the output voltage from the power source to the        driver, in a first condition; and    -   bypassing said up-converter, in a second condition, and        implementing said step of controlling the driver.

Hereinafter, several modes are used for describing in which way thelighting controller is controlling the driver and the up-converter.

The lighting system according to embodiments of the invention comprisesthe above lighting controller, and a power source, an up-converter, abypass switch, and one or more drivers with lighting units such as LEDlamps. As shown in FIG. 1, the power source is preferably a battery orbattery set such as that charged by photovoltaic cells during day timeand discharges to power road lamps in evening/night time.

Preferably, the first condition and the second condition are determinedby the occupancy state of the space that is to be illuminated. Forexample when people are more, more light is generally expected;otherwise when few or no people is there, less light is just enough.This occupancy state can be detected by occupancy sensors.Alternatively, for outdoor application such as road lighting, campuslighting or park lighting, the evening/night time can indirectly reflectthe occupancy state: in evening till mid-night there is more occupancyand from mid-night till dawn, less or no people is there; and justbefore dawn more people may come out. Also, in day time there is no needto turn on the light.

Thus, the lighting controller can use an RTOS (Real-time operatingsystem) based timer or simple hour-minute timer. The timing flowchartcan be shown in FIG. 2. The timer starts at dusk, at this time theup-converter is turned on in the loop, and the driver and lamp operate,thus a high light output is provided. This way of controlling can becalled as mode I. After a predefined time from dusk, the time reaches aset value Ts1 which indicates the mid-night. Then system is switched tomode II wherein the up-converter is bypassed. The timer may be rest.After another predefined time from mid-night, the time reaches a setvalue Ts2 which indicates just before the dawn. Then the up-converter isin the power loop again and the lighting unit may again output fullbrightness, and the system works in mode I again. When the natural lightis equivalent to dawn, namely it is dawn, the lighting system can stopfrom providing light and wait until dusk again.

FIG. 3 also shows the transition between mode I and mode II depending onhigh occupancy or low occupancy. In the mode I, the up-converter canboost the battery voltage and provide a 220V DC voltage on the DC gridto the driver; in the mode II, the up-converter is bypassed, and thevoltage from the power source that is 60V is provided on the DC grid.The lighting unit is dimmed down after sensing the lower input voltageto the driver, preferably with change in frequency. Assume the driverhas an efficiency of 85% at non-dimmed state, the overall efficiency is80% (0.85*0.95) without bypassing the up-converter and no-dimming thedriver. It has experimental fact and the inventors verified in lab thatthe efficiency of LED driver decreases by at least 5% at 30% dimminglevel. In case of maintaining the up-converter and dimming the driver,additional loss of efficiency to the tune of 5-7% at reduced dimminglevel, and overall system efficiency decreases to 72% (0.8*0.9).

Further, FIG. 3 shows how the lighting controller switches between modeII and mode III depending on the energy level or output voltage in thepower source/battery. In mode II, that is mid-night time till dawn, theoutput voltage from the battery is originally 60V. The duty cycle of thedriver is set to a certain value to obtain a desired output lumen thatis less than the full brightness output in mode I.

After a certain time's consumption, the energy in the battery ispartially consumed, and this usually leads to the decrease of the outputvoltage of the battery. Set a threshold of 45V for this output voltage,and before the output voltage of the battery drops below this threshold,the lighting controller will control the driver to deliver a constantpower to the lighting unit regardless of how the power source is beingconsumed. More specifically, as the voltage decrease from 60V to 45V,the duty cycle of the driver is increased such that constant power isdelivered. Additionally, during this decrease from 60V to 45V, thevoltage may not continuously decrease but may be stable at some voltagefor a while, and in this while the duty cycle of the driver is alsomaintained such that constant power is delivered. In turn, in mode II,the normal lighting requirement is met via a constant lumen output. Morespecifically, the driver can have a voltage detection circuit to detectthe voltage, and increases its duty cycle proportional to the decreasein battery voltage. Alternatively, the controller can determine a dutycycle proportional to the decrease in battery voltage and notify thedrivers about this determined duty cycle.

Additionally, as the voltage of the battery further drops, there is arisk that the energy in the battery is completely consumed before thedesired ending time, such as dawn. Such problem may occur in case thatthe solar cell does not store enough energy into the battery if the daytime is cloudy. If the energy in the battery is completely consumed, nolight output can be obtained and a black out occurs. To avoid this,after the voltage of the battery drops below 45V, the lightingcontroller enters mode III wherein it controls the driver to deliver agradually reduced power to the lighting unit. More specifically, thecontroller can maintain or decrease the duty cycle of the driver tomaintain or decrease the rate that power is drawn from the battery.Therefore the power delivered to the lighting unit is gradually reducedas the voltage of the battery decreases and the rate is maintained ordecreased. Alternatively, in case the driver is a linear driver, thelighting controller can maintain or increases the conductivity of thelinear power switch. More specifically, the controller can notify thedriver to maintain its duty cycle. Alternatively, the controller cannotify the drivers about one constant duty cycle. The lighting systemcan even switched back to mode II if the output voltage recovers to 45Vbecause additional backup battery is switched in.

Further, as the voltage of the battery still drops for example below42V, the battery voltage may fluctuate, namely decrease and increase ina fast manner that results flicker of the lighting unit perceptible byhuman. To avoid this, the controller may fine tune the duty cycle of thedriver such that the driver delivers the gradually reduced andunfluctuated power to the lighting unit. More specifically, thecontroller may itself or control the driver record the power deliveredin a previous instant, for example 10 ms ago, and try to regulate thepower, delivered at a subsequent instant, as the same or similar as therecorded one despite whether the battery voltage changes or not. If thebattery voltage does not fluctuate, the duty cycle of the driver at thesubsequent instant is maintained; if the battery voltage fluctuates, theduty cycle of the driver at the subsequent instant can be tuned inreverse direction. It should be understood that the fine tuning toeliminate fluctuation is in the micro/short term perspective, and in themacro/long term perspective the power is still gradually decrease. Tothis end, the average duty cycle is maintained or decrease in a slowmanner, and the extent of fine tuning may be within a certain percentageof the average duty cycle, such as positive and minus 10% to 20%.

Further, just before the dawn, the lighting controller can enter mode Iagain by switching the up-converter back to the loop. The up-convertercan boost the output voltage of the battery to 200V and deliver it viathe DC grid to the driver and lighting unit. The lighting controller mayalso notify the driver to work in its normal full bright state, forexample to use its normal duty cycle.

Following will describe some embodiment of the driver and theup-converter.

FIG. 4 shows a typical driver for LED as the lighting unit. It is aflyback converter. There is a driver controller, for example a dedicatedcontrol IC for flyback converter which controls the duty cycle D of thepower switch Si according to the input voltage on DC grid as well as theLED current and LED voltage. In mode II, the duty cycle D can becontrolled to increase as the input voltage on DC grid decreases. Inmode III, the duty cycle D can be maintained or decrease. In mode III,the average of the duty cycle D can be maintained and the duty cycle Dcan be fine tuned within a certain percentage. The principle of flybackconverter is well known and the specification would not give moredetailed elucidation. Alternatively, other kinds of LED driver are alsoapplicable, such as buck converter or boost converter.

FIG. 5 shows an embodiment of the up-converter with a bypass diode thatcan bypass the up-converter. This up-converter may be in a flyback form.The power switch at the primary side is controlled to deliver a boostedvoltage at the secondary side, in mode I. And in mode II, the powerswitch can be disabled and the bypass diode may deliver the batteryvoltage directly to the DC grid.

FIG. 6 shows an alternative embodiment of the up-converter, which is aboost converter. In mode I, the power switch can be controlled to closeand open to boost the battery voltage to the output capacitor Co. Inmode II, the power switch can be kept open and the battery voltage isfed directly to the output capacitor Co and to the DC grid.

Embodiments of the invention can be used in solar based outdoor lightinge.g. street lighting, campus lighting. This proposed system will findgood application in Outdoor Lighting System as it will be at least 8-10%more efficient than conventional static DC grid Outdoor Lighting Systemand 15% more efficient than AC grid Outdoor Lighting System.

The invention has been described in connection with an LED lightingarrangement. However, it can be applied to a driver for other types oflighting technology. For example, other solid state lightingtechnologies may be used. It should also be understood that the abovespecific voltage values are just for example, and for different batterysystem or battery chemistry these values will change.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. The mere fact that certain measures are recited inmutually different dependent claims does not indicate that a combinationof these measured cannot be used to advantage. Any reference signs inthe claims should not be construed as limiting the scope.

The invention claimed is:
 1. A lighting controller, comprising: adetector adapted to detect an output voltage of a power source, saidpower source being configured to provide power to a lighting unit via alighting driver; a controlling unit, coupled to the lighting driver andconfigured to: switch an up-converter between the power source and thelighting driver to boost an output voltage from the power source to thelighting driver, in a first condition; and bypass said up-converter in asecond condition and control the lighting driver to deliver a constantpower to the lighting unit regardless of power consumption of the powersource by the lighting driver, before the detected output voltagedecreases to less than a first threshold, and control the lightingdriver to deliver a gradually reduced power to the lighting unit afterthe detected output voltage decreases to less than the first threshold;wherein said first condition comprises operation of the lighting deviceduring a predetermined period starting at dusk, and wherein said secondcondition comprises operation of the lighting device during a remainingpart of the night other than the predetermined period.
 2. The lightingcontroller according to claim 1, wherein said controlling unit isadapted to: maintain or increase a duty cycle of the lighting driver soas to control the lighting driver to deliver a constant power; andmaintain or increase the duty cycle of the lighting driver so as tocontrol the lighting driver to deliver a gradually reduced power.
 3. Thelighting controller according to claim 2, wherein the controlling unitis further adapted to: fine tune the duty cycle of the lighting driversuch that the lighting driver delivers the gradually reduced powerwithout fluctuation to the lighting unit, after the detected outputvoltage decreases to less than a second threshold less than said firstthreshold.
 4. The lighting controller according to claim 1, wherein thecontrolling unit is further adapted to control a duty cycle of theup-converter, the up-converter comprises an isolated boost converter,the controlling unit further comprises a diode forwarded between aninput and an output of the up-converter.
 5. The lighting controlleraccording to claim 1, wherein the controlling unit is further adapted tocontrol a duty cycle of the up-converter, the up-converter comprises anon-isolated boost converter wherein the controlling unit furthercomprises a boost diode forwarded from a connection point of an inductorand a switch of the boost converter to an output capacitor of the boostconverter.
 6. A lighting system, comprising: a power source; an upconverter coupled with the power source; a lighting driver coupled tothe up converter; a lighting unit coupled to the driver; and thelighting controller according to claim 1, with the detector coupled tothe power source and the controlling unit coupled to the up converterand to the lighting driver.
 7. A method for controlling lighting, themethod comprising: switching an up-converter between a power source anda lighting driver to boost an output voltage from the power source, in afirst condition, said power source providing power to a lighting unitvia the lighting driver; bypassing said up-converter in a secondcondition, and detecting the output voltage of a power source,controlling the lighting driver to deliver a constant power to thelighting unit regardless of power consumption of the power source by thelighting driver before the detected output voltage decreases to lessthan a first threshold, and controlling the lighting driver to deliver agradually reduced power to the lighting unit after the detected outputvoltage decreases to less than the first threshold; wherein said firstcondition comprises operation of the lighting device during apredetermined period starting at dusk, and wherein said second conditioncomprises operation of the lighting device during a remaining part ofthe night other than the predetermined period.
 8. The method accordingto claim 7, wherein controlling the driver to deliver the constant powercomprises maintaining or increasing a duty cycle of the lighting driver;and controlling the lighting driver to deliver a gradually reduced powercomprises maintaining or decreasing the duty cycle of the lightingdriver.
 9. The method according to claim 8, further comprising: finetuning the duty cycle and frequency of the lighting driver such that thelighting driver delivers the gradually reduced power without fluctuationto the lighting unit, after the detected output voltage decreases toless than a second threshold less than said first threshold.